As part of the migration, these links to legal-related subjects
should be updated to the new handbook site.

Drop the scope of this merge request to be nothing but changing
the URLs in the metadata to be correct, and then fixing any trailing
space problems so lefthook will pass.

That makes this first MR easier to review, and the remaining hits
are ones that we ACTUALLY need to review by hand.

Update format for admin and api docs

Because for now, we're changing the format.

Related to: https://gitlab.com/gitlab-org/gitlab-docs/-/issues/1751

In https://gitlab.com/gitlab-org/gitlab/-/merge_requests/118296, we
rate limited the [delete member API](https://docs.gitlab.com/ee/api/members.html#remove-a-member-from-a-group-or-project) but the limit for too low for some self-managed users.
So here we're making it configurable.

Changelog: added

Changelog: changed

Restructure some pages to make the move fit better

Update the links in all user and admin pages

Organizations can facilitate the responsible disclosure of security
issues by providing public contact information. The standard way to do
this is by using a [security.txt](https://securitytxt.org/) file.

This MR introduces this feature by adding:

- a new application setting (text, max 2048 chars)
- updated admin UI to configure this instance-level setting
- updated application setting API to configure the setting
- a new controller to render the content when present
- updated documentation describing the feature and how to use it

When present, the content will be available at
`https://YOUR_INSTANCE/.well-known/security.txt`.
Authentication is not required to view this file.

Changelog: added

This is not used on the current docs website
and needs to be removed for future compatibility
with Hugo.

Changelog: other

Add CI/CD for github to registration features

Changelog: changed
EE: true

Because it's now on the left sidebar

Related to: https://gitlab.com/gitlab-org/gitlab/-/issues/433313

Add merge pipelines to registration features

Changelog: changed
EE: true